Finding net gravitational force magnitude on moonby TmrK Tags: force, gravitational, magnitude, moon 

#1
Sep1311, 11:41 PM

P: 21

1. The problem statement, all variables and given/known data
The drawing (not to scale) shows one alignment of the sun, earth, and moon. The gravitational force that the sun exerts on the moon is perpendicular to the force that the earth exerts on the moon. The masses are: mass of sun=1.99 × 1030 kg, mass of earth=5.98 × 1024 kg, mass of moon=7.35 × 1022 kg. The distances shown in the drawing are rSM = 1.50 × 1011 m and rEM = 3.85 × 108 m. Determine the magnitude of the net gravitational force on the moon. 2. Relevant equations F_{sm}=Gm_{s}m_{m}/r_{sm}^{2} F_{em}=Gm_{e}m_{m}/r_{em}^{2} F_{net}=F_{sm}+F_{em} 3. The attempt at a solution Solved for Fsm, which equals to 4.3359444667x10^{64} Fem=1.977847934X10^{84} After finding the sum of these two forces, which is 8.68x10^{128}, I decided to find the square root of this and ended up getting 2.946183972531247x10^{64}. This, however, was proven incorrect. 



#2
Sep1311, 11:56 PM

Emeritus
Sci Advisor
PF Gold
P: 5,198

The forces aren't in the same direction, so you can't just add their magnitudes together. You need to find their vector sum.
EDIT: Also you should really include units in all of your calculations. 



#3
Sep1411, 12:16 AM

P: 21

It's that, or WileyPlus's system... 


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